To make the simple syrup:
Pour equal parts sugar and water in a small sauce pan over medium heat. Stir until the sugar has dissolved into the water.
Add the Jalapeno slices (including seeds and membrane) and remove from the heat. Set aside until cooled.
Pour the syrup into a mason jar, or sealed container until ready to use.
For a salted rim:
Pour salt onto a plate and rub a sliced lime along the rim of your glass. Dip the rim into the plate of salt.
Into a cocktail glass add simple syrup, fresh squeezed lime juice, jalapeno slices and tequila
Add enough ice to fill the glass and then pour in grapefruit juice and top off with a splash of soda